The present disclosure deals with issues of coherent demodulation of high order signal constellations, such as N-Quadrature Amplutude Modulation (N-QAM) where N is an integer, in phase noise environments.
One way to perform phase tracking of carrier recovery loop in coherent demodulation of high order QAM signal constellations is to periodically insert pilot symbols of lower constellation order, e.g. a 4-QAM pilot for a 64-QAM transmission. The reason is reduction in decision errors of these low-constellation order symbols compared to the symbols used for the payload transmission. The lower error probability is used in the carrier recovery, e.g. by applying a higher weight for such pilot symbols in phase error tracking determination.
A problem with existing technology is that the carrier recovery may produce fairly long error bursts due to the inherent drawbacks in phase error tracking on these symbols, and another problem is that introduction of more pilots scavenge the payload, i.e. traffic throughput is reduced.